Conventionally, gas sensors are mounted on, for example, an exhaust system of an engine exhaust pipe or the like and utilized for detecting particular gas components in an exhaust gas. Among these gas sensors, there is known a gas sensor in which a detection element having at least one or more cell provided with a pair of electrodes on a surface of a solid electrolyte body; and a heater are integrally laminated.
In the gas sensor having such a configuration, since a solid electrolyte body is exposed to side faces of a detection element, conductive substances, such as soot, contained in exhaust gas are tend to adhere to the solid electrolyte body. In this case, in the solid electrolyte body to which soot adheres, leak current caused by the soot is generated in a portion achieving the temperature lower than the temperature which burns off the soot (about 600 degrees C.) as well as generating oxygen ion conductivity of the solid electrolyte body (e.g., 200 to 600 degrees C.). As a result, gas concentration detection performance deteriorates.
Thus, a technique has been developed in which a paste mainly made of alumina is applied to an exposed portion of the solid electrolyte body achieving at a temperature of below 600 degrees C. when a gas sensor element is in use (e.g., refer to Patent Document 1).